This paper analyzes the evolution of U.S. patent law between the first patent act in 1790 and 1870, the passage of the last major patent act of the nineteenth century. During most of the nineteenth century, patent law developed in the courts, and instrumental to this development were a relatively small patent bar, a subset of the judiciary, and several repeat parties who played a role in a significant proportion of patent cases. Yet at several junctures, most importantly with the major changes introduced in 1836, but also through minor statutory changes throughout the nineteenth century, Congress intervened to alter the patent statute.

We argue that this evolution is best understood through an interest group-based analysis, focused on the question of the choice of which institution interest groups select in their efforts to alter the law. The courts and Congress each present interest groups with a different menu of costs and benefits. Although the federal courts have generally been viewed as relatively costly to capture, we argue that the nineteenth century federal bench was less costly to influence than Congress in many instances. A relatively few judges heard the vast majority of patent cases, allowing the patent bar to seek change through the courts.

There were two major and several minor patent statutes, as well. Interest groups turned to Congress for two reasons. First, despite the general agreement among bench and bar on the appropriate evolutionary path for patent law, there remained in American law a powerful strain of anti-monopoly thought, hostile to patents. Although most patent cases ended up litigated before sympathetic judges by the skilled patent bar, not every patent case did so and the proportion being litigated outside the small strata of experienced judges grew over time. And, because of the "democratic" nature of patent practice, patent law touched individuals spread across the country and made litigation before judges with an anti-monopoly orientation a real risk. Interest groups therefore turned to Congress on occasion to "lock in" changes in the law that they had achieved through the courts. They also sought Congressional aid in correcting occasional dead-ends reached in the law's development.